On the latest version of the Gill AC there are 5 BNC connectors, as opposed to 3 BNC connectors on older models. WE1, WE2 and WE sense have now been split to individual connectors.
WE sense is the sense lead for WE1, it must be connected to WE1 at the cell. WE sense is used to eliminate voltage drop across the WE1 cable.
WE2 must never be connected to WE1 or WE sense.